Arterial blood, which supplies the heart muscle, is able to pass through healthy heart tissue while nourishing the same, yet has difficulty reaching ischemic tissue. As a result, the supply of ischemic tissue with nutrients and the discharge of metabolic catabolites from such ischemic tissue will be impaired.
In this context, it has already been proposed to supply ischemic tissue with blood through retrograde perfusion. This means that blood is tried to be allowed to flow back from the coronary sinus through the coronary venous system in counterflow by feeding blood from a different source into the coronary sinus, either by permanently connecting an artery with the coronary sinus or by temporarily inserting a catheter into the sinus, which catheter is supplied with blood taken from a remote artery and transported by the aid of a blood pump located outside the patient's body.
Another technique proposed for retroperfusion uses an inflatable balloon which is fixed to the end of a catheter to intermittently occlude the coronary sinus. The blood pressure in the coronary sinus rises during the occlusion at every heart beat so as to cause blood reaching the coronary sinus through the healthy tissue of the heart muscle to be flushed back into the ischemic tissue. For such an intermittent coronary sinus occlusion, the balloon end of the catheter is inserted either percutaneously or surgically. The other end of the catheter is supplied with a gas or fluid by a pump which causes the cyclic inflation and deflation of the balloon.
A typical application of blood retroinfusion in coronary veins through intermittent coronary sinus occlusion applies to myocardial protection during a short-term coronary arterial occlusion in the context of a cardiologic intervention. A typical such intervention comprises, for instance, the balloon dilatation of an arteriosclerotically constricted coronary artery. That method, which is also known as percutaneous transluminal coronary angioplasty (PTCA), comprises the conduction of a balloon catheter into the region of the coronary artery stenosis under X-ray control and the compression of the osclerotic plaque by the inflation of the balloon, which is located on the end of the catheter. During the dilatation of the balloon, no supply of the tissue with oxygen-containing blood takes place downstream in the artery with functional changes in the ischemic area of the myocard being detectable already at dilatations lasting longer than 30 seconds. Consequent″ial problems of the ischemic protection of the myocard will also be faced with at other interventions aimed at coronary vascularization such as, e.g., atherectomy, coronary endoprostheses, laser applications and percutaneous valvular surgeries.
A device for the retroinfusion of coronary veins is, for instance, known from EP 230 996 A2, by which a pressure-controlled, intermittent coronary sinus occlusion can be performed. The device comprises a means for occluding the sinus such as, e.g., an inflatable balloon catheter, a pressure measuring unit for measuring the fluid pressure within the coronary sinus and a control unit which generates triggering signals for the occlusion device to trigger or release an occlusion. The control unit is devised in a manner that the pressure maximum in the coronary sinus is measured during every heart beat, a plateau value of the pressure maxima of consecutive heart beats is estimated by calculation and the occlusion of the coronary sinus is released on the basis of the plateau value of the pressure maxima.
The occlusion of the coronary sinus causes a pressure increase and, as a result, a retroperfusion of blood via the respective vein into the nutritive capillaries of the ischemic area so as to enable the supply of nutrients to that area. At a release of the occlusion, the retroperfused blood is flushed out with the metabolic waste products being carried off at the same time. In the method according to EP 230 996 A2, a systolic pressure curve is, thus, estimated based on the measurement of the pressure maximum in the coronary sinus during every heart beat, whereby the occlusion of the coronary sinus is released as a function of the plateau value of the systolic pressure curve.
In order to determine the time at which the occlusion is to be triggered again, an empirically acquired formula is proposed according to the method of EP 230 996 A2, which allows for an estimation of the interval between the end of the occlusion and the peak value of the reactive hyperemia. This empirically acquired formula is based on parameters of the systolic and diastolic pressure curves determined for the occluded coronary sinus, with a linear regression being performed subsequently. By the method according to EP 230 996 A2 it has become possible to retrigger the occlusion only after the occurrence of the peak value of the reactive hyperemia, i.e. after the impounded blood has streamed out of the coronary sinus. Yet, due to the inaccuracy of the empirically determined formula, the time until the next occlusion of the coronary sinus will occasionally be chosen too long for safety reasons, which means that it will be waited too long “before triggering the next occlusion. That method has, thus, become inefficient, apart from the fact that the calculational implementation of the method has turned out to be cumbersome and not accomplishable at an adequate speed.